The principal objective of this research project jis the characterization of the dynamic state of biological membranes. Particular emphasis will be placed on teh interrelation between cell surface lateral diffusion and systematic flow, with the ultimate goal of relating these properties to specific intracellular interactions and cell functions. For this purpose, a number of systems, amenable for study, have been identified in which there is clear evidence of the spontaneous and/or ligand-induced redistribution of cell surface receptors. These are: (a) locomoting fibroblasts, (b) chemotactic polymorphonuclear leukocytes (PMN's), (c) cells in mitosis, and (d) cells polarized by microtubule disrupting agents. In the long term, a better understanding of these systems may have implications to such diverse areas as the invasiveness of neoplastic cells, and the resistance to infection. The principle physical technique to be used in these studies is fluorescence redistribution after photobleaching (FRAP). In the FRAP technique, the lateral transport of fluorescently labeled membrane-bound probes is characterized through measurements of the surface distribution as a function of time after an initial, localized or patterned, photobleaching pulse. Work will also continue on the development and application of a new technique, fluorescence photobleaching anisotropy (FPA), designed to characterize the physical state of membranes with accurate determinations of structural order parameters.